#include <iostream>
#include <vector>
#include <map>
using namespace std;

map<char, vector<char>> dict;

void createDict()
{
    dict.clear();
    dict['2'].push_back('a');
    dict['2'].push_back('b');
    dict['2'].push_back('c');
    dict['3'].push_back('d');
    dict['3'].push_back('e');
    dict['3'].push_back('f');
    dict['4'].push_back('g');
    dict['4'].push_back('h');
    dict['4'].push_back('i');
    dict['5'].push_back('j');
    dict['5'].push_back('k');
    dict['5'].push_back('l');
    dict['6'].push_back('m');
    dict['6'].push_back('n');
    dict['6'].push_back('o');
    dict['7'].push_back('p');
    dict['7'].push_back('q');
    dict['7'].push_back('r');
    dict['7'].push_back('s');
    dict['8'].push_back('t');
    dict['8'].push_back('u');
    dict['8'].push_back('v');
    dict['9'].push_back('w');
    dict['9'].push_back('x');
    dict['9'].push_back('y');
    dict['9'].push_back('z');
}

void dfs(int cur, int max , string tmp, string digits, vector<string> &res){
    if( cur == max ){
        res.push_back(tmp);
        return;
    }
    for (int i = 0 ;i < dict[digits[cur]].size();i++){
        dfs (cur+1 , max , tmp+dict[digits[cur]][i], digits,res);
    }

}

vector<string> letterCombinations(string digits) {

    string tmp = "";
    vector<string> res;
    createDict();
    dfs(0,digits.length(),tmp,digits,res);
    return res;
}

int main (){
    string digits = "23";
    vector<string> res = letterCombinations(digits);
    for(int i = 0 ; i < res.size();i++)
        cout << res[i] << " ";

}
